The present invention relates generally to electric motors, and particularly to winding arrangements and methods of fabricating and operating single phase induction motors.
Induction motors of the resistance start, induction run variety, also known as resistance split phase motors, are used in a number of applications such as refrigerators, freezers, furnaces, dehumidifiers, and pumps. Typically, such motors are provided with a main winding and a start winding with the start winding being deenergized during the running condition of the motor. The start winding is typically switched out of the motor circuit as the motor approaches running speed by a switching device, such as a current activated relay, a centrifugal switch, a voltage operated switch, or a magnetically operated switch.
Resistance start, induction run motors generally utilize the resistance of the start winding to achieve the desired current phase displacement between the current of the main winding and the current of the start winding for starting the motor. The necessary resistance is often achieved by providing a plurality of coils with each comprising a predetermined number of forward conductor turns, which are distributed in selected slots of a magnetic core, and providing an auxiliary coil by winding a conductor in a direction reverse from that of the forward wound coils of the start winding. The magnetic effect of the reverse wound coil is essentially cancelled by increasing the number of the effective forward wound turns of one of the start coils by the same number of effective turns.
This magnetic field cancelling effect may also be provided by winding the start winding in two parts and then disposing the two parts in a magnetic core such that the magnetic fields produced thereby are in a bucking relationship. From the standpoint of terminology, subsequent discussion of reverse turns or reverse wound coil or coils is intended to mean turns or coils formed by either winding in a direction opposite the forward wound coils of a start winding, or turns or coils formed separately from the remaining coils of a start winding but disposed and corrected in a magnetic core in a manner so as to produce bucking magnetic fields.
Because of the decreasing availability of energy and the concomitant sharp increase in cost, increased efforts have been made to improve motor efficiencies with much of the effort being directed toward the design of capacitor run motors for applications in which resistance start, induction run motors have been used previously. Even though capacitor run motors increase motor operating efficiency, the design and manufacture of typical capacitor run motors represents a considerable added expense over resistance start, induction run motors, thus limiting the applications where capacitor run motors are economically feasible. The economic feasibility of utilizing a capacitor run motor in lieu of a resistance start, induction run motor is especially limited in situations where the capacitor run motor is designed to approach balanced operation in order to optimize operating efficiency. Furthermore, it is known that typical capacitor run motors often encounter problems resulting from the inherent low starting torque of such motors.
Efforts have been made to broaden the range of applicability of capacitor run motors by developing starting arrangements to increase their starting torque. For example, externally connected resistors have been connected in series with the start winding and a relay for disconnecting the externally mounted resistor, during the run condition of the motor. However, the adding of an externally mounted resistor represents still another expense or additional cost which even further limits the applications in which capacitor run motors can be economically substituted for resistance start, induction run motors.
It is desirable, therefore, to develop winding and connection arrangements for single phase induction motors which would improve their operating efficiency at a minimum of cost, thereby permitting their use in a wide variety of applications currently being served by resistance start, induction run motors. Furthermore, it is desirable to develop single phase motors which would not suffer from low starting torque and the relatively high cost associated with typical capacitor run motors.
As discussed previously, many single phase induction motors are fabricated with a start winding resistance to provide the desired phase displacement for motor starting. This resistance is achieved either by providing a start winding having both forward and backward wound conductor turns, or by providing a two part start winding wherein the respective parts are wound and disposed on the magnetic core so that their respective magnetic fields are in a bucking relationship. However, the backward wound or disposed turns must either be removed from the motor circuit during the run condition or a relatively large run capacitor must be utilized in order to improve motor operating efficiency.
One known approach for partially solving some of the previously discussed problems associated with the use of a start winding having a reverse wound or disposed portion in a capacitor run motor is disclosed in Houtman U.S. Pat. No. 4,107,583, which issued on Aug. 15, 1978 and is assigned to the assignee of the present invention. The entire disclosure of the Houtman patent is incorporated herein by reference. This patent discloses, among other things, a connection arrangement wherein the reverse wound or disposed portion of the start winding is disconnected during the running condition of the motor, thereby improving motor operating efficiency while obtaining a relatively high starting torque for the motor.
It is desirable, however, to even further increase motor operating efficiencies of single phase induction motors without greatly increasing their cost. Furthermore, it is desirable to retain the starting characteristics or torque of the resistance start, induction run motors, thereby eliminating any need for externally mounted resistors to obtain an acceptable starting torque. Still further, it would be desirable to develop winding and connection arrangements which would use capacitors to increase motor efficiency, particularly in the run condition, wherein the capacitor size could be minimized and, thus, reduce the cost necessary to obtain such improved efficiencies.
Accordingly, it is an object of the present invention to provide new and improved dynamoelectric machine winding and connection arrangements which improve operating efficiency.
Another object of the present invention is to provide new and improved winding connection arrangements and operating methods for single phase conduction motors which can be readily and economically employed to increase motor efficiencies in applications typically served by resistance start, induction run motors.
Yet another object of the present invention is to provide new and improved capacitor run induction motors which maximize winding utilization and improve motor performance without the necessity of any external resistance for the purpose of starting.
A further object of the present invention is to provide new and improved winding and interconnection arrangements for use with conventional resistance start, induction run motors to improve efficiency.
A still further object of the present invention is to provide new and improved operating methods and winding connection arrangements for use with conventional resistance start, induction run motors which optimize the employment of capacitors and which reduce the capacitor requirements necessary to obtain an optimum improved efficiency with such conventional motors.
In the resistance start, induction run motors discussed above that employ reverse wound or disposed coils for increasing the resistance of the start winding, the reverse wound or disposed coil is typically positioned in the same slots as one of the forward wound coils of the start winding. In some cases, however, two reverse wound coils have been utilized because of insufficient slot space to accommodate the necessary number of reverse conductor turns, and "spill over" into adjacent slots occurred. Thus, the turns of the "backlash winding", as the backward or reverse wound turns are often called, have been concentrated in one pair of slots, normally the slots for the outermost coils, with some of the windings spilling over into the adjacent slot pair. The problem with such a concentration of backlash turns is that it causes the end turns thereof about the faces of the core to protrude outside the available mounting space. This is particularly troublesome in motor applications where space is at a premium, such as, for example, hermetic compressors. This exceeding of available mounting space is especially great when some or all of the motor windings are made of aluminum rather than copper because of the increased wire size in aluminum in order to provide the necessary amount of current carrying capacity.
A large number of concentrated conductor turns also presents problems in injecting such turns into the slots of the magnetic core. Large slot fill increases the probability of turns of conductors being inadvertently moved outside the insulating wedges which are utilized to electrically insulate the conductors in a slot from the bore of the core. Also, an increase in injection pressure is often required to insert the large number of conductor turns into the slots thereby increasing the likelihood of damage to the wire or conductor turns.
It is, therefore, an object of the present invention to provide an induction motor and methods for fabricating same in which the peak end turn factor of windings thereof is reduced to facilitate mounting of the motors.
A further object of the present invention is to provide new and improved methods of fabricating single phase induction motors which facilitate winding placement and minimize or eliminate damage to the windings during placement.
A still further object of the present invention is to provide an improved single phase induction motor and method of fabricating the same in which more desirable winding harmonics is achieved.
An additional object of the present invention is to provide an improved single phase induction motor wherein the winding harmonics can be reduced and/or distributed in a manner whereby improved operation of the motor is realized.